Mother Nature cranking up the heat in southwestern US
By
Alex Sosnowski, AccuWeather senior meteorologist
Published Apr 28, 2021 4:33 PM EDT
|
Updated Apr 30, 2021 6:25 PM EDT
Hot and dry weather is again expected to build across the southwestern United States as April draws to a close and May begins, but is there any hope of relief from the North American monsoon this summer?
Phoenix will make a run at the 100-degree F mark Friday, Saturday and Sunday. Temperatures are forecast to reach at least as high as the middle to upper 90s over the three-day stretch. Not only will the temperature be significantly higher than average, but the triple-digit heat is arriving earlier than the average date of May 2.
The normal high for Phoenix at the end of April is in the upper 80s. Highs expected into this weekend will be more typical of late May and early summer.
Despite some recent surges of heat, the Valley of the Sun has not yet hit the century mark this year. The highest temperature recorded so far in 2021 was 98 on April 4.
Over the years, the temperature has hit 100 on nearly every date in April and has hit 105 on multiple dates. The earliest in the year the city has hit 100 was on March 26, 1988.
And the building heat will be much more expansive than just across the Phoenix area, as temperatures will spike to above-normal levels from California to New Mexico and Colorado across much of the Northwest and northern Rockies late this week.
A northward bulge in the jet stream will suppress storms and cloud cover for several days. A broad area of temperature departures of 10-20 degrees above average for late April are predicted.
For example, in Salt Lake City, the normal high is in the middle 60s in late April. Temperatures are forecast to surge into the 80s by Friday and may even challenge the daily record of 84 set in 1959.
It is likely to be a similar story for much of the southwestern U.S. late this week. Friday record highs may be challenged in Los Angeles and Palm Springs, California; Las Vegas and Reno, Nevada; and Flagstaff and Yuma, Arizona, to name a few.
On Saturday, the jet stream is forecast to begin to collapse over the northern part of the Western states, causing temperatures to drop a bit. At the same time, heat will linger over the interior Southwest.
Temperatures are forecast to climb to within a few degrees of record high levels for the date in portions of Arizona, New Mexico and Colorado.
"We expect a gradual increase in the flow of marine air across coastal California as the weekend progresses," AccuWeather Senior Meteorologist Dan Pydynowski said. "This should allow temperatures to ease back in places such as Los Angeles and San Diego."
Highs are forecast to trend from near 90 Friday to the 70s over the weekend in L.A. and from the upper 70s Friday to the 60s in San Diego late this weekend.
The scarce rainfall in the region is one of the key factors behind the unusual hot spell. When the ground is dry, more of the sun's energy is available to heat the ground and lower part of the atmosphere. When the ground is wet, less of the sun's energy is available for heating as it is used up during the evaporation process.
The rainfall deficit in the Southwest has its roots back through last summer. From June 1, 2020, through April 29, 2021, Phoenix has only picked up 32% or 2.51 inches of its normal of 7.89 inches of rain.
Much of the Southwest has faced similarly dismal precipitation amounts, and drought conditions began worsening last summer as a result. In Arizona alone, all of the state is considered to be abnormally dry, with nearly 60% of the state in exceptional drought, the highest level of drought, according to the United States Drought Monitor.
In fact, 63% of the western U.S. is in the grips of severe drought and more than 20% of the region is facing exceptional drought.
North American monsoon outlook
The bulk of the rain in the Desert Southwest tends to occur in two seasons, during the winter from storms that move in from the Northern Pacific and the monsoon which brings moisture northward from the Gulf of Mexico and sometimes the tropical Pacific during summer. Neither of these weather players has brought meaningful rain to the parched West.
The North American monsoon is brought on by a persistent area of high pressure over multiple layers of the atmosphere that sets up over the western U.S. during the summer months.
CLICK HERE FOR THE FREE ACCUWEATHER APP
It is exactly where this high sets up that greatly determines how much moisture will get pumped into the Southwest, AccuWeather Long-Range Meteorologist Brandon Buckingham said.
While most people associate large storm systems as a pumping mechanism for moisture, high pressure areas can do that as well over time. Moisture can be drawn in and recycled on a daily basis beneath the large, clockwise flow around high pressure.
"If the high sets up rather far west like it did in 2020, the flow of moisture from the Gulf of Mexico is cut off and thunderstorm activity tends to be limited over the Southwest, but if the high sets up farther to the east, the door is opened for moisture to flow in from the Gulf of Mexico and a more generous amount of thunderstorm activity tends to occur," Buckingham explained.
"Last year the high expanded and was centered rather close to the Pacific coast of the U.S, but this year we expect the high to be centered over the northeastern Rockies and central Plains," AccuWeather Lead Long-Range Meteorologist Paul Pastelok stated.
The door should be opened for Gulf of Mexico moisture to flow into the Southwest, ushering in higher humidity levels that could lead to nearly daily showers and thunderstorms, especially during July and August.
Pacific waters cooled down off the coast of the Northwest over winter, and that's a good signal to meteorologists that the high pressure area will reside farther away from the West Coast this year, according to Pastelok.
But that position and hope for beneficial rain is not set in stone and AccuWeather's long-range forecasting team still has some concerns for precipitation prospects in the Southwest this summer.
Monsoon storm clouds move into the metro area above the Holy Family Catholic Church Wednesday, July 11, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
"Waters off the Northwest coast are now starting to warm gradually," Pastelok said. "If they warm too much, our concern is the high pressure might slide back toward the Pacific coast again, which could hurt the Southwest monsoon."
As the weather pattern continues to evolve from a spring pattern to a summer one in the western U.S., there may be another opportunity or two for some moisture from Pacific storms to arrive. If that were to happen, showers could dampen lower elevations and rain and wet snow could occur in the mountains over the next month or so.
Undulations in the jet stream will also allow heat and cool air to change hands in the coming weeks, and even when the monsoon arrives, there could be some ongoing concerns.
"The monsoon will not end the drought in the Southwest, but will bring some relief from the heat," Pastelok explained, adding that any rain could bring temporary relief. Prior to the substantial uptick of humidity levels and more widespread downpours, the onset of monsoon could spell dangers like lightning-ignited wildfires and dust storms, referred to as haboobs, that could develop as thunderstorms strike the Southwest.
Just this week, AccuWeather released its summer outlook for the U.S., with more insights on the weather conditions and fire danger expected in the coming months.
Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.
Report a Typo
News / Weather Forecasts
Mother Nature cranking up the heat in southwestern US
By Alex Sosnowski, AccuWeather senior meteorologist
Published Apr 28, 2021 4:33 PM EDT | Updated Apr 30, 2021 6:25 PM EDT
Hot and dry weather is again expected to build across the southwestern United States as April draws to a close and May begins, but is there any hope of relief from the North American monsoon this summer?
Phoenix will make a run at the 100-degree F mark Friday, Saturday and Sunday. Temperatures are forecast to reach at least as high as the middle to upper 90s over the three-day stretch. Not only will the temperature be significantly higher than average, but the triple-digit heat is arriving earlier than the average date of May 2.
The normal high for Phoenix at the end of April is in the upper 80s. Highs expected into this weekend will be more typical of late May and early summer.
Despite some recent surges of heat, the Valley of the Sun has not yet hit the century mark this year. The highest temperature recorded so far in 2021 was 98 on April 4.
Over the years, the temperature has hit 100 on nearly every date in April and has hit 105 on multiple dates. The earliest in the year the city has hit 100 was on March 26, 1988.
And the building heat will be much more expansive than just across the Phoenix area, as temperatures will spike to above-normal levels from California to New Mexico and Colorado across much of the Northwest and northern Rockies late this week.
A northward bulge in the jet stream will suppress storms and cloud cover for several days. A broad area of temperature departures of 10-20 degrees above average for late April are predicted.
For example, in Salt Lake City, the normal high is in the middle 60s in late April. Temperatures are forecast to surge into the 80s by Friday and may even challenge the daily record of 84 set in 1959.
It is likely to be a similar story for much of the southwestern U.S. late this week. Friday record highs may be challenged in Los Angeles and Palm Springs, California; Las Vegas and Reno, Nevada; and Flagstaff and Yuma, Arizona, to name a few.
On Saturday, the jet stream is forecast to begin to collapse over the northern part of the Western states, causing temperatures to drop a bit. At the same time, heat will linger over the interior Southwest.
Temperatures are forecast to climb to within a few degrees of record high levels for the date in portions of Arizona, New Mexico and Colorado.
"We expect a gradual increase in the flow of marine air across coastal California as the weekend progresses," AccuWeather Senior Meteorologist Dan Pydynowski said. "This should allow temperatures to ease back in places such as Los Angeles and San Diego."
Highs are forecast to trend from near 90 Friday to the 70s over the weekend in L.A. and from the upper 70s Friday to the 60s in San Diego late this weekend.
The scarce rainfall in the region is one of the key factors behind the unusual hot spell. When the ground is dry, more of the sun's energy is available to heat the ground and lower part of the atmosphere. When the ground is wet, less of the sun's energy is available for heating as it is used up during the evaporation process.
The rainfall deficit in the Southwest has its roots back through last summer. From June 1, 2020, through April 29, 2021, Phoenix has only picked up 32% or 2.51 inches of its normal of 7.89 inches of rain.
Much of the Southwest has faced similarly dismal precipitation amounts, and drought conditions began worsening last summer as a result. In Arizona alone, all of the state is considered to be abnormally dry, with nearly 60% of the state in exceptional drought, the highest level of drought, according to the United States Drought Monitor.
In fact, 63% of the western U.S. is in the grips of severe drought and more than 20% of the region is facing exceptional drought.
North American monsoon outlook
The bulk of the rain in the Desert Southwest tends to occur in two seasons, during the winter from storms that move in from the Northern Pacific and the monsoon which brings moisture northward from the Gulf of Mexico and sometimes the tropical Pacific during summer. Neither of these weather players has brought meaningful rain to the parched West.
The North American monsoon is brought on by a persistent area of high pressure over multiple layers of the atmosphere that sets up over the western U.S. during the summer months.
CLICK HERE FOR THE FREE ACCUWEATHER APP
It is exactly where this high sets up that greatly determines how much moisture will get pumped into the Southwest, AccuWeather Long-Range Meteorologist Brandon Buckingham said.
While most people associate large storm systems as a pumping mechanism for moisture, high pressure areas can do that as well over time. Moisture can be drawn in and recycled on a daily basis beneath the large, clockwise flow around high pressure.
"If the high sets up rather far west like it did in 2020, the flow of moisture from the Gulf of Mexico is cut off and thunderstorm activity tends to be limited over the Southwest, but if the high sets up farther to the east, the door is opened for moisture to flow in from the Gulf of Mexico and a more generous amount of thunderstorm activity tends to occur," Buckingham explained.
"Last year the high expanded and was centered rather close to the Pacific coast of the U.S, but this year we expect the high to be centered over the northeastern Rockies and central Plains," AccuWeather Lead Long-Range Meteorologist Paul Pastelok stated.
The door should be opened for Gulf of Mexico moisture to flow into the Southwest, ushering in higher humidity levels that could lead to nearly daily showers and thunderstorms, especially during July and August.
Pacific waters cooled down off the coast of the Northwest over winter, and that's a good signal to meteorologists that the high pressure area will reside farther away from the West Coast this year, according to Pastelok.
But that position and hope for beneficial rain is not set in stone and AccuWeather's long-range forecasting team still has some concerns for precipitation prospects in the Southwest this summer.
Monsoon storm clouds move into the metro area above the Holy Family Catholic Church Wednesday, July 11, 2018, in Phoenix. (AP Photo/Ross D. Franklin)
"Waters off the Northwest coast are now starting to warm gradually," Pastelok said. "If they warm too much, our concern is the high pressure might slide back toward the Pacific coast again, which could hurt the Southwest monsoon."
As the weather pattern continues to evolve from a spring pattern to a summer one in the western U.S., there may be another opportunity or two for some moisture from Pacific storms to arrive. If that were to happen, showers could dampen lower elevations and rain and wet snow could occur in the mountains over the next month or so.
Undulations in the jet stream will also allow heat and cool air to change hands in the coming weeks, and even when the monsoon arrives, there could be some ongoing concerns.
"The monsoon will not end the drought in the Southwest, but will bring some relief from the heat," Pastelok explained, adding that any rain could bring temporary relief. Prior to the substantial uptick of humidity levels and more widespread downpours, the onset of monsoon could spell dangers like lightning-ignited wildfires and dust storms, referred to as haboobs, that could develop as thunderstorms strike the Southwest.
Just this week, AccuWeather released its summer outlook for the U.S., with more insights on the weather conditions and fire danger expected in the coming months.
Related:
Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.
Report a Typo